Process absorption spectrometer

ABSTRACT

The aim of the invention is to reduce the apparatus-related complexity and the mounting effort in a process absorption spectrometer taking in situ measurements. Said aim is achieved by providing the process absorption spectrometer with a unit comprising a source of radiation and at least one additional unit encompassing a detector, both units being embodied as pieces of field equipment and being connected to a field bus.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2004/003473, filed Apr. 1, 2004 and claims the benefitthereof. The International Application claims the benefits of Germanapplication No. 10314793.4, filed Apr. 1, 2003, both applications areincorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a process absorption spectrometer.

SUMMARY OF THE INVENTION

The principle of the absorption spectroscopy relates to the selectiveabsorption of radiation of a specific wavelength by means of specificgases (gas molecules), in particular in the near infrared range (NIR).The radiation absorption results in the emergence of a spectrum which ischaracteristic for the gas in question. If a spectrometer issuccessfully selectively adjusted to the spectrum which is to beassigned to a specific gas, the received measurement signal isproportional to the number of molecules which are located in ameasurement volume (measurement cell) between a source of radiation anda detector of the spectrometer. Methods known for industrial gasanalysis are for instance non-dispersive infrared (NDIR) spectroscopy,Fourier transform infrared (FTIR) spectroscopy and diode laserspectroscopy.

With the so-called in-line measurement or in-situ measurement, themeasurement cell of the spectrometer is either directly integrated intothe measurement gas flow or the line carrying the measurement gas, e.g.a pipe or a chimney, functions itself as a measurement cell. The sourceof radiation and the detector, or several detectors in the case ofmulti-channel measurements, are thus arranged at different locations inthe process plant, to which end the spectrometer is subdivided into twoor more sub-devices. These sub-devices are connected to one another viaspecial coupling lines, so that they can function as one completedevice. The coupling lines and the signals passing over them aredesigned in this case to suit the specific technology or device (e.g.hybrid cable with electrical lines and fiber optic lines). The provisionof and cable laying for this type of special lines involves acorresponding outlay.

The underlying object of the invention is thus to reduce theapparatus-related complexity and the mounting effort in in-situabsorption spectrometers.

According to the invention the object is achieved by means of a processabsorption spectrometer having a unit containing a source of radiationand at least one additional unit containing a detector, both units beingdesigned as pieces of field equipment and being connected to a fieldbus. As the units of the spectrometer according to the invention aredesigned as pieces of field equipment, they can be installed,parameterized and operated in a process plant and/or a processautomation system in the same manner as any other pieces of fieldequipment without any additional effort. In particular, the cablingarrangements for them are standard as with other pieces of fieldequipment.

Corresponding to an advantageous development of the spectrometeraccording to the invention, the additional unit containing the detectorcontains means to generate a measurement result from measurement signalsof the detector and additional signals, which are transmitted from theunit containing the source of radiation to the additional unitcontaining the detector. The additional signals can for example bereference signals which were acquired in the unit containing the sourceof radiation by reference measurement of a reference gas and arenecessary for the generation of the measurement result.

These reference signals can be transmitted in an advantageous mannerfrom the unit containing the source of radiation via the field bus tothe additional unit containing the detector. This can be effected by aso-called slave-slave communication for instance. This function is oneof those provided by the ‘Profibus’ field bus and can also be referredto as data cross-traffic. The communication between the units designedas pieces of field equipment and the process controller takes placeaccording to the master-slave principle, i.e. a designated device ispresent in each instance in the process controller, said speciallyselected device being the master, which operates the field bus,parameterizes the slaves (pieces of field equipment) assigned to it andcarries out the data exchange in a cyclical operation. In the case ofthe data cross-traffic, specific data, in this case additional signals,are not exchanged using the indirect route via the master, but insteaddirectly between the slaves, thereby resulting in a reduced load on themaster and a reduction in the time taken for the data transmission. Thebus cycle does not significantly lengthen, any required mixture ofmaster-slave and cross-traffic relationships is possible.

Alternatively or in addition to the transmission via the field bus, thesource of radiation can be advantageously modulated with the additionalsignals, with the additional signals in the additional unit beingseparated from the measurement signals of the detector by means ofdemodulation. The modulation thus takes place such that the selectiveabsorption of the radiation in the measurement gas is not impaired. Byway of example, in the case of a diode laser spectrometer, with which aspectral line of the measurement gas is cyclically scanned in awavelength dependent manner, the modulation with the additional signalscan take place in an area of the scanning lying outside the spectralline or in the gaps between successive scanning cycles.

With a further embodiment of the spectrometer according to theinvention, the means for generating the measurement result from themeasurement signals of the detector can be arranged in the unitcontaining the source of radiation, in which case the measurementsignals are transmitted from the additional unit containing the detectorto the unit containing the source of radiation via the field bus.

The spectrometer according to the invention is described below withreference to an exemplary embodiment shown in the drawing.

BRIEF DESCRIPTION OF THE DRAWING

The sole FIG. 1 shows an exemplary embodiment of the inventiveabsorption spectrometer.

DETAILED DESCRIPTION OF INVENTION

The process absorption spectrometer shown as a greatly simplified blockdiagram comprises a unit 1 which comprises a continuously variable diodelaser as a source of radiation 2, and a unit 3, which contains aphotoelectrical detector 4. Both units 1 and 3 are designed respectivelyas pieces of field equipment and are connected via communication devices5 and/or 6 to a field bus 7 in a process automation system of which onlya master device 8 is shown here.

The unit 1 of the spectrometer further contains a controller device 9,which operates a modulation device 10 for wavelength-dependentmodulation of the source of radiation 2. The light beam 11 emitted bythe source of radiation 2 is fed to the detector 4 in the further unit 3by means of a radiation divider 12 partially via a glass fiber 13 onto amonitor detector 14, via a further glass fiber 15 through a referencegas cell 16 filled with a reference gas onto a reference detector 17 andfrom the unit 1 through a measurement gas 18, in a pipe or chimney forinstance. The measurement signals generated by the detector 4 areevaluated in an evaluation device 20 arranged downstream together withfurther signals to form a measurement result which is visualized on theone hand on a display 21 of the unit 3 and on the other hand istransmitted in the process automation system via the communicationdevice 6. The additional signals mentioned, which are needed to generatethe measurement result, are the reference signals of the referencedetector 17, the monitor signals of the monitor detector 14 andinformation relating to the modulation of the source of radiation 2.These additional signals are generated in the unit 1 and are transmittedto the field bus 7 via the controller device 9 and the communicationdevice 5 in order to receive the additional unit 3 from thecommunication device 6 and forward it to the evaluation device 20. Thecommunication between the two units 1 and 3 thus takes place directly,i.e., by avoiding the master 8, according to a slave-slave transmissionmethod also referred to as a data cross-traffic.

In addition or alternatively the additional signals can also betransmitted via the light beam 11 directly between the two units 1 and3. The diagram shows how the source of radiation 2 is cyclicallycontrolled by the modulation device 10 by means of a ramp-shapedincreasing flow 1 in order to scan a spectral line 22 of the measurementgas 18 in a wavelength-dependent manner. The additional signals to betransmitted from the unit 1 to the unit 3 can then be remodulated in anarea 23 of the scanning lying outside the spectral line 22 or inscanning gaps 24 between successive scannings.

Alternatively to the exemplary embodiment shown, the evaluation device20 and the display device 21 can be arranged in the unit 1 containingthe source of radiation 2, with which the measurement signals of thedetector 4 are then transmitted from the additional unit 3 to the unit 1containing the source of radiation 2 by means of the field bus 7.

The power can be supplied to units 1 and 3 separately or likewise viathe field bus 7.

1.-6. (canceled)
 7. A process absorption spectrometer comprising: afirst unit containing a source of radiation; and at least one secondunit containing a detector, wherein the first and the second units aredesigned as field devices and are connectable to a field bus.
 8. Theprocess absorption spectrometer according to claim 7, wherein the secondunit comprises a mechanism to generate a measurement result frommeasurement signals of the detector and from signals transmitted fromthe first unit to the second unit.
 9. The process absorptionspectrometer according to claim 8, wherein the signals are at leastpartially transmittable via the field bus.
 10. The process absorptionspectrometer according to claim 9, wherein the first and the secondunits are designed to communicate with one another via the field busaccording to a slave-slave transmission method.
 11. The processabsorption spectrometer according to claim 7, wherein the source ofradiation is modulated with at least one part of signals transmittedfrom the first unit to the second unit, and wherein in the second unitthe signals transmitted from the first unit to the second unit areseparated from measurement signals of the detector by demodulation. 12.The process absorption spectrometer according to claim 8, wherein thesource of radiation is modulated with at least one part of signalstransmitted from the first unit to the second unit, and wherein in thesecond unit the signals transmitted from the first unit to the secondunit are separated from measurement signals of the detector usingdemodulation.
 13. The process absorption spectrometer according to claim9, wherein the source of radiation is modulated with at least one partof signals transmitted from the first unit to the second unit, andwherein in the second unit the signals transmitted from the first unitto the second unit are separated from measurement signals of thedetector by using demodulation.
 14. The process absorption spectrometeraccording to claim 10, wherein the source of radiation is modulated withat least one part of signals transmitted from the first unit to thesecond unit, and wherein in the second unit the signals transmitted fromthe first unit to the second unit are separated from measurement signalsof the detector by demodulation.
 15. The process absorption spectrometeraccording to claim 7, wherein the first unit comprises means forgenerating a measurement result from measurement signals of thedetector, and wherein the measurement signals are transmittable from thesecond unit to the first unit via the field bus.
 16. The processabsorption spectrometer according to claim 8, wherein the first unitcomprises means for generating a measurement result from measurementsignals of the detector, and wherein the measurement signals aretransmittable from the second unit to the first unit via the field bus.17. The process absorption spectrometer according to claim 9, whereinthe first unit comprises means for generating a measurement result frommeasurement signals of the detector, and wherein the measurement signalsare transmittable from the second unit to the first unit via the fieldbus.
 18. The process absorption spectrometer according to claim 10,wherein the first unit comprises means for generating a measurementresult from measurement signals of the detector, and wherein themeasurement signals are transmittable from the second unit to the firstunit via the field bus.
 19. The process absorption spectrometeraccording to claim 11, wherein the first unit comprises means forgenerating a measurement result from measurement signals of thedetector, and wherein the measurement signals are transmittable from thesecond unit to the first unit via the field bus.
 20. A processabsorption spectrometer with a unit containing a source of radiation andat least one additional unit containing a detector, with both unitsbeing designed as pieces of field equipment and being connected to afield bus.
 21. The process absorption spectrometer according to claim20, wherein the additional unit containing the detector contains meansto generate a measurement result from measurement signals of thedetector and additional signals which are transmitted from the unitcontaining the source of radiation to the additional unit containing thedetector.
 22. The process absorption spectrometer according to claim 21,wherein the additional signals are at least partially transmitted viathe field bus.
 23. The process absorption spectrometer according toclaim 22, wherein the two units communicate with one another via thefield bus according to a slave-slave transmission method.
 24. Theprocess absorption spectrometer according to claim 20, wherein thesource of radiation is modulated with at least one part of additionalsignals, and wherein in the additional unit the additional signals areseparated from measurement signals of the detector by means ofdemodulation.
 25. The process absorption spectrometer according to claim20, wherein the unit containing the source of radiation contains meansfor generating a measurement result from measurement signals of thedetector, and wherein the measurement signals are transmitted from theadditional unit to the unit containing the source of radiation using thefield bus.